Draker
Well Known Member
Some people I show my RV to express shock not that I built the airplane, but that I wired it myself. I don't think it's that big a deal--many builders do it. In fact I find it shocking that some builders will buck every rivet in their plane themselves, but shy away from the wiring and end up buying a pre-made harness. DIYing your avionics wiring is a big job, but it's not that difficult. I actually found it to be the most pleasant and mentally stimulating part of the build. It takes patience, attention to detail, and a lot of prep work. Here's how I approached mine:
1. Mission / Requirements / Select primary manufacturer
I knew I wanted a VFR flyer with all the creature comforts including autopilot, electronic trim, big displays, "the works." I did not want to spend a lot of time trying to wrestle with interoperability, so sourcing as much as possible from a single manufacturer was preferred. I also wanted to do some software development and experiment so needed data outputs. I looked at dynon, garmin, and others and chose a package that fit the mission best for me. I won't name the vendor because it's not important for this guide.
2. Component selection
Wrote down a list of every major item needed. Including all avionics, gauges, sensors, goodies and gizmos. Steam gauges, antennas, stick grips (they're wired), lights (interior and exterior), everything. Don't forget the connector kits for each avionics device (they may be sold separately). I ended up keeping this in a tab in a spreadsheet.
3. Block diagram
What needs to connect to what, and what kind of connection is it? This required reading the installation manual for each device and understanding what needs to be connected, how, and whether it's optional or not. Output of this step was a block diagram on the first page of my schematics.
4. Physical diagram
Based on what needed to connect to what, and where I wanted to mount everything in the plane, I planned out where in the airplane each thing goes. This also let me plan which bulkheads wires and tubes needed to run through. The most critical section here tends to be the runs thorough the main spar center section, since a lot of wires have to go through it, and Vans doesn't provide many holes. There is a PDF from Vans (for the RV-7 and RV-9) showing where you can drill more if you need to, but somehow I got away with using the stock holes only. Some things can be mounted anywhere you want, and I chose the locations of those things to minimize wire runs. At this point I also decided what needs to be disconnect-able, because I needed connectors for anything that can be disconnected. Anything that has any potential chance of having to be taken off the airplane (for condition inspection, painting, or any other reason) should get a connector. You don't want to have to cut wires when you take your plane to the paint shop. Physical diagram ended up as page 2 of my schematics.
5. Circuit diagrams
This is by far where most of my time was spent. Downloaded every installation manual for every device and hit the books! Studied each device's pinouts to determine which circuits were needed, and the start and end location (device) for each circuit and each air hose line. I got a bit of a head start here by studying a design from a builder with a similar avionics setup. This is also where I decided which panel switches I needed, and what kind they must be (SPST, SPDT, DPDT, etc.). And what buttons I needed, and what lights I needed, and so on. Seriously, spend time on this. I spent about 3X as much time on the circuit diagrams than I spent on any other avionics task, including physically running the wires. Output was pages 5-20 of my schematics.
6. Circuit list
Once the circuit diagrams were done, I could enumerate each and every circuit in the airplane, give them each a code/name, determine wire gauge based on the current requirements and how long the run will be. Also whether they need to be shielded or not. As a rule of thumb, I shielded everything that carried an analog or digital signal, including and especially audio. I printed each circuit name on heat shrink tube to uniquely label each wire. Don't forget the grounds. I chose to have an independent wire to each tab on the tab forrest, and ended up with a little over 400 circuits. Don't skip this, because you're going to at some point need to answer "which wire out of hundreds is the RS-232 RX wire for my transponder?"
7. Connectors
From here, you know how many pins each connector needs to hold, and what kind of connector it must be, so you can buy them. I went with mostly Deutsch connectors and some circular plastic connectors. I also named/labled each connector to label them physically in the airplane. My list is here. For each connector, I planned which connector pin got which circuit, so they all lined up when I plugged everything in. Don't forget, for shielded wires, you generally want to have a shield drain on each side of the connector, and pin the shield circuit through the connector. Think about which connectors you want free-hanging, and which ones you want as "bulkhead" connectors physically attached to the airframe. I didn't leave many spares (this is probably a mistake) so if I needed to run 6 wires through my wing root and wanted it disconnect-able, I used a 6 place connector.
8. Fuse list
I chose to use fuses instead of circuit breakers, so I planned out where to run each power wire so it was properly fused. For each fuse, I listed which block it belonged in, what position in the block, the fuse rating, the wire gauge, and the circuit name so I can cross reference them. This allowed me to confirm how many fuse blocks I'd need (I put them on the sub-panel).
9. Load analysis
From here, I did a load analysis, listing out the average and max amps drawn by each device, and added up what would be on and off during each phase of flight. This allowed me to a. buy the right size alternator, b. ensure my "keep-alive" bus and the load powered by my battery backup were within those sources' current limits.
10. Misc connectors
I also needed ring, spade, and butt splice connectors, which I listed here.
11. Wire purchase
I put together a spreadsheet to help me estimate the lengths of each circuit run, given which bulkheads they had to go through. With that, and the gauge of each wire, I knew how much I had to buy. Added +30% safety margin to account for screwups, rework, and service loops, and placed the big wire and connector order.
(NOTE all of the above was prep work, before running a single wire or turning a single installation screw)
12. Run the wires
I did not build a full wire harness outside the aircraft and then install it at once. Instead I ran each individual wire separately, labeling each end with printable heat shrink. Secured the wires to the aircraft as needed. Enclosed them in snake skin anti-chafe for any wires that needed to flex or move. Once all the wire ends for a particular connector were done, I pinned the connector and installed the wires into the connector. I tried to not move on to another connector until a full connector was pinned and done, to avoid forgetting one. Once a wire bundle is done, I laced them together every 6 inches or so to keep the bundles nice and neat. I generally tried to work back-to-front. Follow best practices for stripping, crimping pins and attaching shield drains. Remember to use snap bushings, M22529/2 edging, or some other protection whenever a wire goes through a hole in metal, and install the bushings before you run the wires. Always double-check the power wires are pinned correctly at each connector, that's generally where mistakes can cause smoke and cost money.
13. (Optional) Continuity tests and short circuit tests
Once everything is together, you can use a multimeter to ensure that pin X on one device is actually connected to pin Y on the other device. I wouldn't do every circuit, but at least do the power and grounds. Also stick the multimeter between power and ground pins on your devices to make sure there are no short circuits.
14. Turn on
Finally, flip the master switch and verify everything works! Hopefully you were careful and nothing pops or smokes. You can visually check all of your fuses or circuit breakers to make sure none were tripped. Finally, go through the "setup" or "test" procedures for your avionics and make sure you see green checkboxes everywhere you should see them.
Hope this helps someone. Comment below if I forgot anything important, I'll add it to the guide.
1. Mission / Requirements / Select primary manufacturer
I knew I wanted a VFR flyer with all the creature comforts including autopilot, electronic trim, big displays, "the works." I did not want to spend a lot of time trying to wrestle with interoperability, so sourcing as much as possible from a single manufacturer was preferred. I also wanted to do some software development and experiment so needed data outputs. I looked at dynon, garmin, and others and chose a package that fit the mission best for me. I won't name the vendor because it's not important for this guide.
2. Component selection
Wrote down a list of every major item needed. Including all avionics, gauges, sensors, goodies and gizmos. Steam gauges, antennas, stick grips (they're wired), lights (interior and exterior), everything. Don't forget the connector kits for each avionics device (they may be sold separately). I ended up keeping this in a tab in a spreadsheet.
3. Block diagram
What needs to connect to what, and what kind of connection is it? This required reading the installation manual for each device and understanding what needs to be connected, how, and whether it's optional or not. Output of this step was a block diagram on the first page of my schematics.
4. Physical diagram
Based on what needed to connect to what, and where I wanted to mount everything in the plane, I planned out where in the airplane each thing goes. This also let me plan which bulkheads wires and tubes needed to run through. The most critical section here tends to be the runs thorough the main spar center section, since a lot of wires have to go through it, and Vans doesn't provide many holes. There is a PDF from Vans (for the RV-7 and RV-9) showing where you can drill more if you need to, but somehow I got away with using the stock holes only. Some things can be mounted anywhere you want, and I chose the locations of those things to minimize wire runs. At this point I also decided what needs to be disconnect-able, because I needed connectors for anything that can be disconnected. Anything that has any potential chance of having to be taken off the airplane (for condition inspection, painting, or any other reason) should get a connector. You don't want to have to cut wires when you take your plane to the paint shop. Physical diagram ended up as page 2 of my schematics.
5. Circuit diagrams
This is by far where most of my time was spent. Downloaded every installation manual for every device and hit the books! Studied each device's pinouts to determine which circuits were needed, and the start and end location (device) for each circuit and each air hose line. I got a bit of a head start here by studying a design from a builder with a similar avionics setup. This is also where I decided which panel switches I needed, and what kind they must be (SPST, SPDT, DPDT, etc.). And what buttons I needed, and what lights I needed, and so on. Seriously, spend time on this. I spent about 3X as much time on the circuit diagrams than I spent on any other avionics task, including physically running the wires. Output was pages 5-20 of my schematics.
6. Circuit list
Once the circuit diagrams were done, I could enumerate each and every circuit in the airplane, give them each a code/name, determine wire gauge based on the current requirements and how long the run will be. Also whether they need to be shielded or not. As a rule of thumb, I shielded everything that carried an analog or digital signal, including and especially audio. I printed each circuit name on heat shrink tube to uniquely label each wire. Don't forget the grounds. I chose to have an independent wire to each tab on the tab forrest, and ended up with a little over 400 circuits. Don't skip this, because you're going to at some point need to answer "which wire out of hundreds is the RS-232 RX wire for my transponder?"
7. Connectors
From here, you know how many pins each connector needs to hold, and what kind of connector it must be, so you can buy them. I went with mostly Deutsch connectors and some circular plastic connectors. I also named/labled each connector to label them physically in the airplane. My list is here. For each connector, I planned which connector pin got which circuit, so they all lined up when I plugged everything in. Don't forget, for shielded wires, you generally want to have a shield drain on each side of the connector, and pin the shield circuit through the connector. Think about which connectors you want free-hanging, and which ones you want as "bulkhead" connectors physically attached to the airframe. I didn't leave many spares (this is probably a mistake) so if I needed to run 6 wires through my wing root and wanted it disconnect-able, I used a 6 place connector.
8. Fuse list
I chose to use fuses instead of circuit breakers, so I planned out where to run each power wire so it was properly fused. For each fuse, I listed which block it belonged in, what position in the block, the fuse rating, the wire gauge, and the circuit name so I can cross reference them. This allowed me to confirm how many fuse blocks I'd need (I put them on the sub-panel).
9. Load analysis
From here, I did a load analysis, listing out the average and max amps drawn by each device, and added up what would be on and off during each phase of flight. This allowed me to a. buy the right size alternator, b. ensure my "keep-alive" bus and the load powered by my battery backup were within those sources' current limits.
10. Misc connectors
I also needed ring, spade, and butt splice connectors, which I listed here.
11. Wire purchase
I put together a spreadsheet to help me estimate the lengths of each circuit run, given which bulkheads they had to go through. With that, and the gauge of each wire, I knew how much I had to buy. Added +30% safety margin to account for screwups, rework, and service loops, and placed the big wire and connector order.
(NOTE all of the above was prep work, before running a single wire or turning a single installation screw)
12. Run the wires
I did not build a full wire harness outside the aircraft and then install it at once. Instead I ran each individual wire separately, labeling each end with printable heat shrink. Secured the wires to the aircraft as needed. Enclosed them in snake skin anti-chafe for any wires that needed to flex or move. Once all the wire ends for a particular connector were done, I pinned the connector and installed the wires into the connector. I tried to not move on to another connector until a full connector was pinned and done, to avoid forgetting one. Once a wire bundle is done, I laced them together every 6 inches or so to keep the bundles nice and neat. I generally tried to work back-to-front. Follow best practices for stripping, crimping pins and attaching shield drains. Remember to use snap bushings, M22529/2 edging, or some other protection whenever a wire goes through a hole in metal, and install the bushings before you run the wires. Always double-check the power wires are pinned correctly at each connector, that's generally where mistakes can cause smoke and cost money.
13. (Optional) Continuity tests and short circuit tests
Once everything is together, you can use a multimeter to ensure that pin X on one device is actually connected to pin Y on the other device. I wouldn't do every circuit, but at least do the power and grounds. Also stick the multimeter between power and ground pins on your devices to make sure there are no short circuits.
14. Turn on
Finally, flip the master switch and verify everything works! Hopefully you were careful and nothing pops or smokes. You can visually check all of your fuses or circuit breakers to make sure none were tripped. Finally, go through the "setup" or "test" procedures for your avionics and make sure you see green checkboxes everywhere you should see them.
Hope this helps someone. Comment below if I forgot anything important, I'll add it to the guide.
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